In fabricating a semiconductor device, in some cases, a process for attaching two or more devices is required. An example of such a process that requires a process for attaching two or more devices is a process for manufacturing a silicon-on-insulator (SOI) substrate, or a process for forming a stack-type semiconductor device for improving a degree of integration. These processes require a process for attaching two or more devices, for example, attaching substrates to each other by using an adhesive, or directly attaching substrates by using a eutectic characteristic arising due to the diffusion between metal layers that constitute the substrates, without use of an adhesive. Regarding the method of attaching substrates by using an adhesive, an organic or inorganic adhesive layer is formed on a surface of a substrate, and then, the substrate is attached to another substrate due to an adhesive force of the adhesive, and regarding the direct-attaching, pressure is applied to substrates at a temperature that is equal to or higher than a eutectic point of the substrates to attach the substrates to each other.
From among the attaching methods, according to the latter method, as illustrated in FIG. 1A, substrates are taken away from cassettes (C1, C2, C3, through Cn) by using a robot (R), and then, to-be-attached substrates are pre-aligned in a pre-aligning device (P.A), and then, a pair of substrates are accurately aligned in chambers (CH1, CH2, CH3, through CHn) and pressure is applied thereto at a temperature that is equal to or higher than a eutectic point to attach the substrates to each other. However, when substrates are independently attached in the respective chambers (CH1, CH2, CH3, through CHn), since the attaching process is intermittently performed, a time for attaching several substrates is long. In addition, as illustrated in FIG. 1B, when several pairs of substrates are placed in a single chamber (CH) and the attaching process is simultaneously performed thereon, a process time is relatively reduced. However, the attaching process performed in the chamber (CH) has a substantially low degree of accuracy. In addition, when the size of the chamber (CH) is increased to perform the substrate attaching process with high accuracy, a chamber occupies a relatively large space and corresponding installation and maintenance costs substantially increase compared to the manufacturing efficiency of the attached substrates.